JPH0996704A - Fresnel lens and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make light be incident on a Fresnel surface side and to prevent the generation of ghosts. SOLUTION: This Fresnel lens is composed of a main body provided with a flat surface 18a and a Fresnel surface 18b provided with cyclic elevated parts 19, the respective elevated parts 19 are provided with a flat peak part 19a almost parallel to the flat surface 18a and at least one slope 19b extended from the flat peak part to the flat surface 18a and a light shielding layer 19d is provided on the flat peak part 19a of the respective elevated parts. Also, the Fresnel lens is used as the picture enlargement means of the display device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fresnel lens having a light shielding layer and a display device such as a liquid crystal display device using the Fresnel lens as a magnifying element.

[0002]

2. Description of the Related Art A liquid crystal display device can be constructed to be relatively thin and has been applied in many fields. Recently, a projection type liquid crystal display device having a large screen has been developed. A typical projection liquid crystal display device includes a projection lens so as to project a magnified image on a screen. on the other hand,
The image can be magnified using an optical element other than the projection lens.

For example, Japanese Patent Laid-Open No. 5-188340 discloses a projection type liquid crystal display device including a liquid crystal display panel, a Fresnel lens for enlarging an image generated by the liquid crystal display panel, and a screen. . In this case, the projection liquid crystal display device further comprises an array of converging light transmitter elements. Each of the array of convergent light-transmitter elements is suitable for forming an erect image and each of the Fresnel lenses is provided to magnify the image exiting the array of convergent light-transmitter elements. ing.

The converging optical transmission element is a resin or glass rod-shaped transparent body having a diameter of 1 mm to 2 mm, and its refractive index changes in the radial direction, and its length and refractive index distribution are set appropriately. By doing so, an erect image can be formed with one element. A plurality of optical transmission element having the same length and having such properties are arranged in close proximity to each other so as to form a converging optical transmission element array with their end faces aligned, thereby forming a converging optical transmission device. Can be used. An image forming apparatus using such an optical transmission medium array can have a very short focal length as compared with an image forming apparatus using a normal spherical lens, and the optical performance is constant in a row and a plane. There is a great advantage that the distance adjustment between them is unnecessary.

However, when such an optical transmission element array is used as an image-forming device, a single element can obtain an enlarged or reduced image by changing the length of the element. When configured, the images of the respective elements are overlaid and the normal image cannot be obtained. Therefore,
Only the same size image can be obtained for the optical transmitter array,
A means of scaling is required.

In order to solve this, Japanese Patent Publication No. 58-33
Japanese Patent No. 526 and Japanese Patent Publication No. 61-12249,
Disclosed is a magnifying and demagnifying imager using a converging optical transmitter array. These prior arts disclose disposing a convex lens or a concave lens on the emitting end face side or the incident end face side of the converging light transmitting element array. However, in the above-mentioned conventional technique, the convex lens or the concave lens may be a single lens or a compound lens in which a plurality of lenses are combined, and various shapes may be used to achieve a desired magnification. Explaining. However, when such an image forming device is used as a magnifying optical system in a liquid crystal display device, for example, the image on the screen corresponding to the central part of the liquid crystal panel and the image on the screen corresponding to the peripheral part have a resolution M.
The problem of changing TF occurred.

[0007]

The resolution MTF is 4 (l
It was found that 50% or more under the condition of (p / mm) is a good image formation state. However, it is difficult to achieve the resolution MTF of 50% or more in the above-mentioned conventional technique, and in order to achieve this, the angle of light passing through the peripheral portion of the liquid crystal panel with respect to the normal line of the liquid crystal panel must be about 10 °. I have to. If this angle is small, the enlargement ratio will be considerably small. Therefore, although the converging light transmitting element array itself is suitable for thinning, if a convex lens or a concave lens is used together with the converging light transmitting element array, it is not possible to reduce the thickness of the device.

Therefore, there is a demand for an expanding element which can be used together with a converging light transmitting element array and which can achieve a thin liquid crystal display device. In order to satisfy such a requirement, attention has been paid to the use of a Fresnel lens together with an array of converging optical transmission element, as disclosed in Japanese Patent Laid-Open No. 5-188340.
However, this publication does not explain how to use the Fresnel lens. The inventor of the present application has recently researched a preferable form of a Fresnel lens and found that a preferable display device and a liquid crystal display device can be obtained by using the Fresnel lens thus obtained as a magnifying means. However, a ghost may occur depending on how the Fresnel lens is used.

An object of the present invention is to provide a Fresnel lens which is constructed so that light is incident from the Fresnel surface side thereof and is free from ghost. Another object of the present invention is to provide a display device and a liquid crystal display device provided with an appropriately arranged Fresnel lens.

[0010]

A Fresnel lens according to the present invention comprises a body having a flat surface 18a and a Fresnel surface 18b having periodic ridges 19, each ridge 19 being flat. A flat top 19a approximately parallel to the surface 18a and the flat top 18 from the flat top
at least one sloped surface 19b extending toward a, and a light-blocking layer 19d having the flat top 1 of each of the ridges.
9a is provided.

This configuration is suitable for causing light to enter from the Fresnel surface 18b of the Fresnel lens in the display device. However, the light is passed through the Fresnel surface 18 of the Fresnel lens.
When the light is incident from b, there is a problem that the light incident on the body of the Fresnel lens is undesirably reflected inside the body to cause a ghost. In the above structure, the apex of the raised portion 19 is cut to form a flat top portion 19a, and the light shielding layer 19d is provided on the flat top portion 19a. This prevents the generation of ghosts.

In addition to this, if the width of the flat top portion changes according to the position of the raised portion, the display does not change according to the position of the Fresnel lens. further,
The at least one inclined surface may include a main inclined surface extending to one side of the flat top portion and a main inclined surface of the flat top portion and a sub-inclined surface extending to the other side. This facilitates the manufacture of Fresnel lenses.

In addition, d is the width of the flat top, p is the pitch of the ridges, r is the angle of the principal ray incident on the main body from the main inclined surface with respect to the axis of the main body, and θ ₁ is the flatness. When the angle of the main inclined surface with respect to the surface, θ ₂ is an angle with respect to the axis of the main body of the sub inclined surface, the width of the flat top,

[0014]

[Equation 2] The configuration should be determined by by this,
The characteristics of the Fresnel lens can be brought out better while preventing the occurrence of ghost.

The display device according to the invention also comprises at least one image-modulating element, an array of converging light-transmitting element which receives light from the image-modulating element to form an equal-erect image, and a flat surface. And a body having a Fresnel surface with periodic ridges, each of the ridges extending at least parallel to the flat surface and extending from the flat top toward the flat surface. A fresnel lens having a sloping surface and a light-blocking layer provided on the flat top of each of the ridges, and a screen, the fresnel lens comprising: It is arranged so as to be incident on the Fresnel surface from the array.

In this case, the at least one image modulation element comprises a plurality of liquid crystal display panels, and the array of converging optical transmission element and Fresnel lens are provided corresponding to each liquid crystal display panel. It is preferable to have a structure.

According to the configurations of the display device and the liquid crystal display device, the Fresnel lens is used as the image enlarging means, and the difference in resolution between the central portion and the peripheral portion of the screen is small, and a ghost-free image is obtained. can get.

[0018]

1 and 2 are views showing a liquid crystal display device 10 according to an embodiment of the present invention. The liquid crystal display device 10 includes four liquid crystal display panels 12. The four liquid crystal display panels 12 are arranged side by side in a square shape. Each liquid crystal display panel 12 includes an effective display area 12a and an ineffective display area 12b around the effective display area 12a. Ineffective display area 12
b is necessary for mounting drive circuit means of liquid crystal and the like. Therefore, if the display is performed in the state of FIG. 2,
The non-effective display area 12b is an area without an image.
In this embodiment, a seamless multi-display device is realized by using the Fresnel lens 18 as an image enlarging means.

In FIG. 1, a backlight 14 is arranged on the front side of the liquid crystal display panel 12. On the rear side of the liquid crystal display panel 12, corresponding to each liquid crystal display panel 12,
A converging optical transmitter array 16 is arranged. The area of each converging light transmitter array 16 is larger than the area of the effective display area 12 a of the liquid crystal display panel 12, and the ineffective display area 12 is
It is smaller than the area including b. Each converging optical transmitter array 1
Reference numeral 6 forms an image of each liquid crystal display panel 12 as an equal-size erect image.

A Fresnel lens 18 is arranged on the rear surface side of each converging light transmitting array 16 in correspondence with each converging light transmitting array 16. As shown in FIGS. 8 and 9, one surface 18a of the Fresnel lens 18 is a flat surface, and the other surface 18b is a undulating Fresnel surface. The Fresnel surface 18b has a concentric raised portion 19,
It has a serrated surface in cross section. Light enters the Fresnel lens 18 from the converging light transmitter array 16. In FIG. 1, the Fresnel surface 18b of the Fresnel lens 18 is arranged toward the incident side, that is, the converging light transmitting element array 16 side. The flat surface 18a of the Fresnel lens 18 is on the emission side.

Further, behind the Fresnel lens 18,
Screen 22 including Fresnel lens 20 for screen
There is. As shown in FIG. 1, the light emitted from the Fresnel lens 18 propagates while spreading, and the adjacent liquid crystal display panel 1
The light emitted from the second effective display area 12a meets the screen 22 without any gap. Therefore, the existence of the non-effective display area 12b of the liquid crystal display panel 12 is invisible to the viewer of the screen 22. In this embodiment, the liquid crystal display panel is used for the display unit, but any image modulation element may be used as long as it is a light emitting type.

FIG. 3 is a diagram showing the features of the convergent optical transmission element 16a that constitutes the convergent optical transmission array 16.
The convergent optical transmission element 16a has a diameter of 1 mm to 2 mm.
In the rod-shaped transparent body made of resin or glass, the refractive index changes in the radial direction as shown in (C).

Incident light entering from the end face of the converging optical transmission element 16a is bent to have a higher refractive index, and as shown in FIG.
It progresses while meandering at a fixed cycle. Then, as shown in FIG. 5, if the lens length Z is appropriately set, an erect real image of equal magnification can be formed at the distance l. In FIG. 6, a large number of converging optical transmission element 16a having the same length are arranged close to each other in a row or a plane with their end faces aligned in parallel to form a converging optical transmission array 16 which is an equal-magnification erecting apparatus. An example is shown. An image forming apparatus using such an optical transmission medium array 16 can have a very short focal length as compared with an image forming apparatus using a normal spherical lens, and its optical performance is constant in rows and planes. There is a great advantage that the distance adjustment between lenses is unnecessary. When such an optical transmission medium array 16 is used as an imaging device, a single element can obtain an enlarged or reduced image by changing the length of the element. The images of the elements overlap and the normal image cannot be obtained. Therefore, only an equal-magnification image can be obtained as an optical transmission element array. Therefore, the Fresnel lens 18 is used here as a means for varying the magnification.

When the Fresnel lens 18 is incorporated into the liquid crystal display device, the Fresnel surface 1 of the Fresnel lens 18 is
8b toward the incident side, or Fresnel surface 18
The resolution especially in the peripheral portion of the scream 22 changes depending on whether or not b is arranged toward the emitting side. The inventor of the present application has found that by arranging the Fresnel surface 18b of the Fresnel lens 18 toward the incident side, the difference between the resolution in the peripheral portion of the scream 22 and the resolution in the central portion of the scream 22 is small, which is desirable. .

FIG. 7 is a diagram for explaining why the resolution in the peripheral portion is lowered when the flat surface 18a is on the incident side and the Fresnel surface 18b is on the outgoing side. As shown in FIG.
It can be seen that the focal length becomes shorter toward the peripheral portion with respect to the focal length of the central portion, and as indicated by the broken line F, the image plane is deviated from the screen 22 and curved. When the cause of the field curvature is analyzed, among rays other than the chief ray having an angle with respect to the optical axis, rays 30 and 31 having the same angle to the principal ray but opposite polarities (the same angle antipolar side ray) The angle difference between the two is small when the light enters the Fresnel lens 18 and becomes large when the light exits the Fresnel lens 18, and the larger the angle between the light ray and the light is on both the incident surface and the emission surface (there is a curvature rather than a flat surface). It was found that the quality becomes more remarkable. Therefore, it was found that in the case of the optical system having the Fresnel surface 18b as the exit surface, the angle difference between the same-angle antipolar sub-rays becomes large and an image is formed in front of the screen 22, thus lowering the resolution. In order to form an image of the central portion and the peripheral portion on a plane, it is necessary to reduce the angular difference between the same-angle antipolar sub-rays in the peripheral portion. Therefore, the bending angle of the chief ray is 13 °
In the above case, the Fresnel surface (curved surface) 18b must be on the incident side.

FIG. 10 is a diagram showing details of the Fresnel lens 18 of FIG. As mentioned above, the Fresnel lens 18
Consists of a body with a flat surface 18a and an undulating Fresnel surface 18b with periodic ridges 19.
Each of the ridges 19 has a flat top 19a approximately parallel to the flat surface 18a and a flat surface 1 from the flat top 19a.
8a and a main inclined surface 19b extending toward 8a. Also,
A sub-slope 19c extends from this flat top 19a on the side opposite to the main slope 19b. In FIG. 10, the sub-inclined surface 19c is shown substantially perpendicular to the flat top portion 19a.

A light shielding layer 19d is provided on each flat top 19a of the ridge 19. Since the flat top portion 19a is parallel to the flat surface 18a, the flat top portion 19a can be easily formed by a printing method. FIG. 11 is a diagram showing a conventional Fresnel lens 18 having a raised portion 19. The flat top 19a of FIG. 10 is the raised portion 19 of FIG.
It can be seen that it was formed by cutting the apex of.

The conventional Fresnel lens 1 shown in FIG.
In No. 8, there is a problem of stray light which causes a ghost. That is, when the light S enters the main inclined surface 19b at a position near the sub inclined surface 19c, this light S is emitted by the sub inclined surface 19c.
At and re-route it in an uncontrolled direction,
Therefore, it causes a ghost. The light shielding layer 19d is provided to solve this problem.

As can be seen from FIG. 8, the shape or inclination of the raised portion 19 is such that the raised portion 19 extends from the center of the Fresnel lens 18.
Changes according to the position of. Therefore, the width of the flat top portion 19a preferably changes according to the position of the raised portion 19.
As shown in FIG. 12, for the manufacturing reason of the Fresnel lens 18, the sub-inclined surface 19 c is actually a flat surface 18.
inclined with respect to a. Needless to say, the main inclined surface 19b located on one side of the flat top portion 19a.
Is formed so that the light mainly enters the main body of the Fresnel lens 18 from the main inclined surface 19b, and the sub inclined surface 19c provided on the other side of the flat top portion 19a actually operates. Is not expected.

The inventor of the present application has found that when the width of the flat top portion 19a is determined by the following relation, the Fresnel lens 1
It has been found that the original action of No. 8 is realized and the ghost can be effectively reduced.

(Equation 3)

Here, d is the width of the flat top portion 19a, p is the pitch of the raised portions 19, r is the angle of the principal ray incident on the main body of the Fresnel lens 18 from the main inclined surface 19b with respect to the axis of the main body, θ ₁ Is the angle of the main inclined surface 19b with respect to the flat surface 18a, and θ ₂ is the angle of the auxiliary inclined surface 19c with respect to the axis of the body of the Fresnel lens 18.

[0032]

As described above, in the Fresnel lens according to the present invention, when light is incident from the Fresnel surface of the Fresnel lens, ghost-free display can be performed. Further, a Fresnel lens can be used as an image magnifying means to realize a ghost-free display device.

[Brief description of drawings]

FIG. 1 is a diagram showing a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a layout view of the liquid crystal display panel of FIG.

FIG. 3 is a diagram showing characteristics of a convergent optical transmission element.

FIG. 4 is a diagram showing light propagation in a convergent optical transmission element.

FIG. 5 is a view showing formation of an equal-size erect image of a convergent optical transmission element.

FIG. 6 shows a converging optical transmitter array.

FIG. 7 is a diagram illustrating a reduction in resolution.

FIG. 8 is a sectional view of a Fresnel lens.

FIG. 9 is a plan view of a Fresnel lens.

FIG. 10 is an enlarged sectional view of a Fresnel lens.

FIG. 11 is a sectional view of a conventional Fresnel lens.

FIG. 12 is a cross-sectional view showing the dimensional relationship of Fresnel lenses.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Liquid crystal display device 12 ... Liquid crystal display panel 16 ... Convergent light transmission body array 18 ... Fresnel lens 18a ... Flat surface 18b ... Fresnel surface 19 ... Raised part 19a ... Flat top part 19b ... Main inclined surface 19c ... Sub inclined surface 19d ... Shading layer

Claims (6)

[Claims] 1. A body comprising a flat surface (18a) and a Fresnel surface (18b) having periodic ridges (19), each of said ridges (19) being said flat surface (18a). ), And a at least one inclined surface (19b) extending from the flat top toward the flat surface (18a), and a light blocking layer (19d) at the ridge. Each said flat top (19a)
Fresnel lens characterized by being provided in. 2. Fresnel lens according to claim 1, characterized in that the width of the flat top (19a) varies according to the position of the ridge (19). 3. The main inclined surface (19b), wherein the at least one inclined surface extends to one side of the flat top portion, and the auxiliary inclined surface (19c), which extends to the other side of the main inclined surface of the flat top portion.
The Fresnel lens according to claim 2, characterized in that 4. d is the width of the flat top (19a), p is the pitch of the ridges (19), r is the angle of the chief ray incident on the body from the main inclined surface (19b) with respect to the axis of the body. , Θ ₁ is the main inclined surface (1
9b), where θ ₂ is the angle of the sub-inclined surface (19c) with respect to the axis of the body, the flat top (1
The width of 9a) is The Fresnel lens according to claim 3, wherein the Fresnel lens is defined by 5. At least one image modulating element (12)
A body having an array (16) of converging light-transmitting element elements that receives light from the image-modulating element to form an erect image of equal size, a flat surface, and a Fresnel surface having periodic ridges. Each of the ridges includes a flat top substantially parallel to the flat surface and at least one ramp extending from the flat top toward the flat surface, the light blocking layer of the ridge being A fresnel lens (18) provided on each of said flat tops and a screen (22), said fresnel lens (18) comprising: said array of light converging light-transmitting element elements (16); A display device, which is arranged so as to be incident on a Fresnel surface (18b). 6. The at least one image modulating element comprises a plurality of liquid crystal display panels (12), the array (16) of converging optical transmitter elements and the Fresnel lens (18).
The liquid crystal display device according to claim 5, wherein and are provided corresponding to each liquid crystal display panel.